1. Field of the Invention
This invention is related to the separation of a gas from a liquid and, more particularly, to the degassification of a seal oil or lubricating oil used in rotating machinery.
2. Background Art
High speed rotating machinery, such as compressors, turbines, or other turbomachinery, typically employs oil or other liquid lubricant based seals and/or bearings around rotating shafts. The working gas moving through or being moved by the rotating machinery will, since it is under pressure, tend to become mixed with and entrained within the liquid lubricant, both reducing the effectiveness of the lubricant and resulting in a loss of the gas. The contaminated lubricant is normally withdrawn on a regular basis and replaced with clean lubricant to maintain optimum operation of the rotating machinery.
The contaminated lubricant can be disposed of, which is wasteful of both the working gas and the lubricant, or can be passed to a degassing tank for the separation of the gas from the lubricant. The separated gas can then be vented to the atmosphere or passed back into the rotating machinery. The clean lubricant can be passed to a holding tank for the lubrication system. Prior patents showing various degassing tank arrangements include U.S. Pat. Nos. 2,570,134; 3,420,434; 4,105,093; 4,477,223; 4,606,652; 4,668,252; and 4,722,663.
The line carrying the recovered working gas from the degassing tank should not pass directly to the rotating machinery without some form of control mechanism. Otherwise, the risk would exist of passing lubricant directly into the gas areas of the rotating machinery, via the degassing tank, and damaging the machinery. In addition, the pressure of the gas released from the degassing tank should be controlled to avoid high pressure damage to downstream equipment. In one prior arrangement, an ejector passed the gas from the degassing tank to a compressor. A control valve, responsive to the pressure of the gas exiting the degassing tank, passed around the ejector and bypassed gas flow to the compressor if the gas pressure was too high. However, this arrangement did not permit proper control with higher gas pressures, particularly when wide pressure variations are present such as during start-up or settle out of the rotating equipment, without using an expensive, high pressure control valve.
It is an object of this invention to separate the entrained gas from a liquid lubricant in rotating machinery and recover and reuse both the gas and lubricant. It is another object to reinject the gas back into the rotating machinery without thereby injecting the lubricant into the rotating machinery. Moreover, it is desirable to provide a control arrangement for reinjecting the recovered gas which is inexpensive and reliable, but which can handle high pressures during start-up, settle out or the like.